Remove mqtt publish templates after 6 months of deprecation

[jbouwh]

Breaking change

The MQTT publish action no longer supports the topic_template and payload_template attributes. In automation and scripts users can use templates by default. Users were instructed to update their automations with a repair flow when the use of the deprecated action options was detected.

Proposed change

Remove mqtt publish templates after 6 months of deprecation

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

Checklist

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[home-assistant]

Hey there @emontnemery, @bdraco, mind taking a look at this pull request as it has been labeled with an integration (mqtt) you are listed as a code owner for? Thanks!

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[jbouwh]

Thanks!